How to bond panels w/parallel feeders?

[gary]

I've been asked to install a 400 amp split bus meter/main panel near the property line next to a utility transformer. The panel will contain two 200 amp main breakers. A large residence some 300' away is to be served from this panel. The GC wants me to run two sets of 4/0 CU feeders in PVC conduits from the service entrance to two 200 amp subpanels mounted next to each other in the garage. One of these panels will be used primarily to serve a possible future pool, spa, secondary buildings etc. Ordinarily I do not run an EGC with the feeders when the house is remote from the service disconnect. But in this case, I'm not sure how to best establish a ground at the house. Should I use two separate #4 Cu Ufer grounds that are bonded together? Would it be better to use a single Ufer ground and simply bond the panels together with a piece of #6 Cu?

 

[bphgravity]

Re: How to bond panels w/parallel feeders?

This may be a bit controversial but, I think you are going to have to provide an equipment ground with each feeder. If not, you will violate the #2 requirement of 250.32(B)(2). The second feeder will provide a metallic path between the the two structures.

 

[gary]

Re: How to bond panels w/parallel feeders?

This may be a bit controversial but, I think you are going to have to provide an equipment ground with each feeder. If not, you will violate the #2 requirement of 250.32(B)(2). The second feeder will provide a metallic path between the the two structures.

Brian, there is only structure involved at this point. The meter/main will be mounted on a pressure treated wood backboard near the road. The two subpanels are to be mounted side by side in the garage of the residence.

 

[iwire]

Re: How to bond panels w/parallel feeders?

The second grounded conductor will be the additional metallic path between structures.

The meter/main mounted on a pressure treated wood backboard near the road is a structure.

[ May 26, 2004, 05:56 PM: Message edited by: iwire ]

 

[websparky]

Re: How to bond panels w/parallel feeders?

Hi Gary,

Let me see if I have this correct.
Utility TFR to a pole mounted type of service disconnecting means rated at 400A. This service disco has two 200A main breakers supplied from the 400A bus.
The underground conductors leave this disco in two conduits, each containing 200A FEEDERS and travels about 300' to individual panels located next to each other in the SAME structure.

215.6 Feeder Conductor Grounding Means.
Where a feeder supplies branch circuits in which equipment grounding conductors are required, the feeder shall include or provide a grounding means, in accordance with the provisions of 250.134, to which the equipment grounding conductors of the branch circuits shall be connected.

When you go to connect the GEC's at this structure,

250.58 Common Grounding Electrode.
Where an ac system is connected to a grounding electrode in or at a building as specified in 250.24 and 250.32, the same electrode shall be used to ground conductor enclosures and equipment in or on that building..............Two or more grounding electrodes that are effectively bonded together shall be considered as a single grounding electrode system in this sense.

you will be installing them like this?

 

[iwire]

Re: How to bond panels w/parallel feeders?

Many times 250.32(B)(2) would allow these feeders to use the grounded conductor as the grounding conductor also. In this installation I agree with Bryan, it would be a violation.

[ May 26, 2004, 06:06 PM: Message edited by: iwire ]

 

[websparky]

Re: How to bond panels w/parallel feeders?

Hi Bob,

250.32 Two or More Buildings or Structures Supplied from a Common Service.

I don't see where this would apply because there is only ONE SERVICE and the structure is supplied by two FEEDERS.

 

[iwire]

Re: How to bond panels w/parallel feeders?

I don't know Dave it sounds to me like two structures, 1) the backboard with the meter main and 2) the main residence, fed from one service.

If this had only one feeder from the meter main at the road to the residence in my opinion, following the rules of 250.32(B)(2) he would not be required to run a EGC at all. At the residence panel he would bond this 3 wire feed just like it came from the utility.

Bob

[ May 26, 2004, 06:22 PM: Message edited by: iwire ]

 

[websparky]

Re: How to bond panels w/parallel feeders?

I don't know Bob, when we consider this being "two" structures, then how does this fit?
225.30 Number of Supplies.

 

[iwire]

Re: How to bond panels w/parallel feeders?

Dave IMO it is two structures, think of the NEC definition of structure.

250.32(B)(2) must apply to feeders as service conductors do not have EGCs run with them.

However you bring up an interesting point with 225.30 it sounds like he can not feed the residence with two 200 amp feeders.

It looks like you had better plan on using these two sets of 4/0 CU feeders in parallel from one 400 amp OCPD and then taping two 200 amp main breaker panels from that 'one' 400 amp feeder.

If you do that you can forget the EGC from meter to house.

 

[hurk27]

Re: How to bond panels w/parallel feeders?

By Bryan The second feeder will provide a metallic path between the the two structures.

If this was true then we would have to always run an EGC to every building, and 230.40 exception 3 would be nothing but a waste of words. Every building will have grounded feeder/service wires common between them, unless it is a ungrounded delta. so how could we use 230.40 excption #3 and still comply with what you said?

 

[gary]

Re: How to bond panels w/parallel feeders?

Thank-you all for the interesting comments!

I don't buy the idea that a meter panel mounted on a backboard out in the open is a "structure."
In this discussion it should be thought of as the "common service." What is so unusual about this situation is that I will be supplying the same building twice from the same common service! If there was only one set of feeders to one subpanel, there is no question that no EGC would be required with the feeders.

 

[hurk27]

Re: How to bond panels w/parallel feeders?

Gary
One thing if you did bring in both feeders to the same building they would have to be in the same location or it would be a violation of 230.72 And also each sub-panel would still have to have a main or it would be a violation of 230.70

[ May 26, 2004, 07:06 PM: Message edited by: hurk27 ]

 

[websparky]

Re: How to bond panels w/parallel feeders?

Hi Guys,

Let's imaging that the AHJ has decided that 225.30 (B)(2) applies here.

This would mean that we now have a definitive "system".
Given that, other requirements also must be fulfilled, right?

 

[gary]

Re: How to bond panels w/parallel feeders?

Gary
One thing if you did bring in both feeders to the same building they would have to be in the same location or it would be a violation of 230.72 And also each sub-panel would still have to have a main or it would be a violation of 230.70

[ May 26, 2004, 07:06 PM: Message edited by: hurk27

Yes, I certainly agree with that.

 

[iwire]

Re: How to bond panels w/parallel feeders?

Originally posted by gary:
I don't buy the idea that a meter panel mounted on a backboard out in the open is a "structure."

You may not want to buy but IMO it is a structure.


Here is the entire NEC definition of structure.

Structure. That which is built or constructed.

We can also look at 225.32 they had to put exceptions to that in order to allow the disconnects for site light poles to be located elsewhere.

The site pole is a structure as defined by the NEC without the exception 3 to 225.32 every light pole would have a disconnect.

 

[gary]

Re: How to bond panels w/parallel feeders?

Hi Guys,

Let's imaging that the AHJ has decided that 225.30 (B)(2) applies here.

This would mean that we now have a definitive "system".
Given that, other requirements also must be fulfilled, right?

Article 225.30 is found immediately below the heading "II. More Than One Building or Other Structure." So I guess we're back to deciding if a panel on a pole is a structure. However, it is starting to look like this is something I'm going to have to discuss with the local AHJ.

 

[iwire]

Re: How to bond panels w/parallel feeders?

Originally posted by gary:
However, it is starting to look like this is something I'm going to have to discuss with the local AHJ.

Probably the best idea in this thread.

[ May 26, 2004, 07:38 PM: Message edited by: iwire ]

 

[gary]

Re: How to bond panels w/parallel feeders?

Probably the best idea in this thread.

Given the wide range of services that are allowed in different areas only you AHJ will have the right answer for you.

I'm very grateful to all of you for your thoughtful replies. Although my original question was about grounding, you've brought up another very important issue I had overlooked ...... multiple feeders to a single building.

 

[hurk27]

Re: How to bond panels w/parallel feeders?

I don't see any requirement for a meter/main combo out at the meter. If you drop a 320 can on the pole with double barrel lugs, and just run the two sets of 4/0 into each main breaker panel (which you will need anyway) this would be the same as the service laterals. Then just a ground rod would be needed at the pole and GEC from one grounding electrode to each panel at the house like it was a split 400 amp service. Otherwize wouldn't 250.24 require the electrode to be taken to the service equipment?